In the realm of scale model rocketry, kit-bashing—using a non-scale sport kit as the basis (or at least as the source of a few parts) for a scale model rocket—is a fairly common practice. It is less common when an existing scale kit can be used to create another scale model, but below is an example of such an opportunity.

The Vostok needs a 9” length of Quest 20 mm T20 body tube, a 2-3/4” length of Estes BT-20 to “sleeve-fit” inside it (9” of BT-20 could work by itself, if built up at the top and bottom ends to fit “centered” inside the plastic rocket body), a motor clip, and a thrust ring. Both models need heat protection to keep the ejection charge and—in composite motors—the “ejection charge after-burn” from warping or melting the plastic; stage couplers or Nomex felt glued inside the body tubes provides insulation. Parachute space is limited inside the Vostok model, which used a 20” parachute; a mylar parachute, or multiple smaller ones, would fit more easily. Both models are heavy for their sizes, as is common for all-plastic model rockets, and they fly best on 18 mm composite "D" motors (or on Estes or Centuri C5-3 black powder motors, *if* one has any) rather than on the MPC-recommended 18 mm C6-4 and/or C9-3 black powder motors (or the "closest-match" Estes or Quest motors). The MPC Titan IIIC kit, however, also offers another scale modeling possibility:

Before the Titan IIIC flew, its three-stage liquid propellant core vehicle (Stage 1, Stage 2, and Stage 3 [the restart-able Transtage]) was test-flown by itself in 1964 and 1965, *without* the two huge solid rocket motors that constituted Stage 0, and these four vehicles were called Titan IIIA (see: http://www.google.com/search?source...0.M g_rR98pRVA ). (This "Stage 0, 1, 2, and 3" numbering system was used in order to avoid confusion in the stage designations of the various Titan III versions that did—and did not—use the solid motors; this stage numbering system is also used today, in Orbital ATK's Minotaur family of launch vehicles, for the same reason.) In addition:

The first Titan IIIA fell short of orbit (but it came close; it accomplished 95% of its test objectives), the second placed a large dummy payload into orbit, and the final two vehicles orbited multiple experimental satellites (the third Titan IIIA orbited the LES 1 "ghost" satellite [see: http://www.google.com/search?ei=Ov_...0. VMhtMpNRrwM ], which in 2013 was discovered to be transmitting again, *46 years* after it went off the air in 1967!). These missions—which involved multiple Transtage maneuvers and engine re-starts—were so successful that a fifth planned Titan IIIA flight was cancelled, and that vehicle was modified to fly later as a Titan IIIC core vehicle. A flying scale Titan IIIA model (or a display-only model, if desired) could be made from the MPC Titan IIIC kit, in the following way:

The main difference between the Titan IIIA and the Titan IIIC was the "A's" lack of the tapered "boat-tail" just above the two Stage 1 engines; like the Titan II ICBM and the Gemini-Titan II, the Titan IIIA's Stage 1 engines and their thrust structure were "hanging in the breeze." For a display-only Titan IIIA model, the boat-tail and the Stage 0 solid motors could simply be left off the core vehicle, which could be painted and "decal-ed" to depict one's favorite Titan IIIA round. To create a *flying* Titan IIIA model, the following modifications could be implemented:

In the MPC Titan IIIC kit, the core vehicle is 1.2 " (30.48 mm) in diameter, which is large enough to accommodate two 13 mm (BT-5) motor mount tubes. As in the old BT-70 size Estes Gemini-Titan II kit (see: http://www.spacemodeling.org/jimz/estes/k-21.pdf ), the Titan IIIA's motor mount tubes could be angled slightly inward toward each other. I don't know what this model's weight would be, but I'm confident that two A10-3T motors would provide good performance; so might two 1/2A3-2T motors.

The 1/100 Vostok had the option of being built for Sputnik 2, not Sputnik 1. Different nose shape and internal details in the nose.

Peter Alway

Thank you for confirming my "temples tingle," Peter. My copy of "Rockets of the World" (in which you depicted both the Sputnik 1 and 2 vehicles, which I couldn't picture in detail in my mind) is packed away at the moment, but the nose profile of the model's optional "Sputnik nose," and the arrangement of the internal chrome "satellite ball" and its associated chrome parts, didn't look quite right for Sputnik 1 to me, but I deferred to the kit's text. The internal satellite parts didn't look quite right for Sputnik 2 either (based on the drawings and museum replicas of it that I've seen), but I figured that MPC may have had to proceed with incomplete or provisional scale data on it, or that the model's size may have forced part production compromises (the satellite-mounting truss structure inside their Titan IIIC's payload fairing doesn't look quite like any that I've seen in pictures, either).

In the MPC Titan IIIC kit, the core vehicle is 1.2 " (30.48 mm) in diameter, which is large enough to accommodate two 13 mm (BT-5) motor mount tubes. As in the old BT-70 size Estes Gemini-Titan II kit (see: http://www.spacemodeling.org/jimz/estes/k-21.pdf ), the Titan IIIA's motor mount tubes could be angled slightly inward toward each other. I don't know what this model's weight would be, but I'm confident that two A10-3T motors would provide good performance; so might two 1/2A3-2T motors.

I didn't comment on this last time, because I wanted to confirm my recollections of some measurements I made of the Titan III C kit a few weeks ago. The MPC kit is undersized by something on the order of 10%-20%. For instance, the boosters, which should be 1.22" in diameter, are about 1.0" in diameter. The core, which should be 1.2" in diameter, is about 1.1" in diameter. The lengths are shorter vaguely in proportion (I haven't specifically measured).

The inside diameter of the core section is about 1.05" in diameter, while two BT-5 tubes would require 2 x 0.541" = 1.82" of space. you'd have to carve away at the paper or the plastic to get that to work, and canting them outward is right out.

All in all, I think it would be about as easy to scratchbuild a flying Titan III A based on Gemini-Titan II plans and a custom conical nosecone.

I didn't comment on this last time, because I wanted to confirm my recollections of some measurements I made of the Titan III C kit a few weeks ago. The MPC kit is undersized by something on the order of 10%-20%. For instance, the boosters, which should be 1.22" in diameter, are about 1.0" in diameter. The core, which should be 1.2" in diameter, is about 1.1" in diameter. The lengths are shorter vaguely in proportion (I haven't specifically measured).

The inside diameter of the core section is about 1.05" in diameter, while two BT-5 tubes would require 2 x 0.541" = 1.82" of space. you'd have to carve away at the paper or the plastic to get that to work, and canting them outward is right out.

All in all, I think it would be about as easy to scratchbuild a flying Titan III A based on Gemini-Titan II plans and a custom conical nosecone.

Peter Alway

I sure wouldn't want to try flying a scale Titan IIIA (using the core vehicle from the MPC Titan IIIC) using two Quest MicroMaxx motors, even though *their* motor mount tubes would fit. :-) Wow--I knew that MPC's regular-construction model rockets (like their 15 mm diameter Miniroc kits) often had "nominal" dimensions (integer-length body tubes--say, an 8" tube--were not uncommonly about 1/4" off), but I never suspected that their plastic ones (they were mainly a plastic model kit manufacturer, after all) were that far off-scale-size! Thank you for letting us know about these size discrepancies (I have two MPC Titan IIIC [and two MPC Vostok/Sputnik] kits, but I haven't built them yet).

Some opinions, please.
What would it take to make these two rockets flyable?
Would using an 18mm D size engine help in the long run to solve the problem?

That is the consensus; other folks have recommended using D10 or D21 composite motors. One consideration (particularly since these motors can have a "flare after-burn effect" after ejection [at least in the re-loadable ones, I think]) that others have mentioned in the MPC Vostok [and Titan IIIC] thread (see: http://www.oldrocketforum.com/showt...74&page=1&pp=10 )--even if one has C5 black powder motors to use (C6s are under-powered for these models)--is that an internal lining in the inner "sleeve" body tube is needed to prevent the heat from soaking through and deforming the outer plastic body. Stage couplers glued inside the inner body tube have been suggested, and I suggested (but have never tried) gluing Nomex felt to the inside of the body tube.